Lazy-fetch the settings for extensions (#38844)

This PR stops us from synchronously initializing the settings page for every extension (including built-in's) on startup. That incurs a small penalty that really adds up the more extensions a user has.

Instead, we'll now only initialize the `CommandSettings` object when we first actually need it. 

From a relatively unscientific test, this saves approximately 10% on the initialization of builtin commands, and for my setup, it trims about 28% off extension initialization (across all built-in's / extensions):

branch | Built-in load (ms) | Extension load (ms) | %Δ builtin | %Δ extensions | 
-- | -- | -- | -- | -- |
main | 1455 | 6867.6 | | |
this PR | 1309.2 | 4919 | -10.02% | -28.37%

Closes #38321

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/CommandSettingsViewModel.cs

@@ -2,18 +2,25 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using ManagedCommon;
 using Microsoft.CmdPal.UI.ViewModels.Models;
 using Microsoft.CommandPalette.Extensions;
 
 namespace Microsoft.CmdPal.UI.ViewModels;
 
-public partial class CommandSettingsViewModel(ICommandSettings _unsafeSettings, CommandProviderWrapper provider, TaskScheduler mainThread)
+public partial class CommandSettingsViewModel(ICommandSettings? _unsafeSettings, CommandProviderWrapper provider, TaskScheduler mainThread)
 {
     private readonly ExtensionObject<ICommandSettings> _model = new(_unsafeSettings);
 
     public ContentPageViewModel? SettingsPage { get; private set; }
 
-    public void InitializeProperties()
+    public bool Initialized { get; private set; }
+
+    public bool HasSettings =>
+        _model.Unsafe != null && // We have a settings model AND
+        (!Initialized || SettingsPage != null); // we weren't initialized, OR we were, and we do have a settings page
+
+    private void UnsafeInitializeProperties()
     {
         var model = _model.Unsafe;
         if (model == null)
@@ -27,4 +34,27 @@ public partial class CommandSettingsViewModel(ICommandSettings _unsafeSettings,
             SettingsPage.InitializeProperties();
         }
     }
+
+    public void SafeInitializeProperties()
+    {
+        try
+        {
+            UnsafeInitializeProperties();
+        }
+        catch (Exception ex)
+        {
+            Logger.LogError($"Failed to load settings page", ex: ex);
+        }
+
+        Initialized = true;
+    }
+
+    public void DoOnUiThread(Action action)
+    {
+        Task.Factory.StartNew(
+            action,
+            CancellationToken.None,
+            TaskCreationOptions.None,
+            mainThread);
+    }
 }